Certain embodiments of this invention relate to an insulating glass (IG) window unit including a heat treatable coating having a silicon (Si) rich silicon nitride inclusive layer in order to achieve desired optical characteristics in the window unit. Other embodiments of this invention relate to a heat treatable coated article including a Si-rich silicon nitride inclusive layer in order to achieve desired color.
Coated articles and IG window units are known in the art. For example, see U.S. Pat. Nos. 5,514,476, 5,800,933 and 6,014,872.
Commonly owned U.S. patent application Ser. No. 09/978,184, filed Oct. 17, 2001 (hereby incorporated herein by reference) discloses a coated article as follows, from the glass substrate outwardly (the top tin oxide layer may be omitted in certain instances) with example thicknesses listed in units of angstroms (xc3x85):
When the aforesaid coated article is coupled with another glass substrate in order to make an IG window unit, the resulting IG window unit (not heat treated (HT)) generally has the following optical characteristics (Ill. C, 2 degree observer):
In Table 2 above, Tvis stands for visible light transmission, and a*t and b*t stand for transmissive (t) a* and b* color values, respectively. Glass side (g) and film side (f) values are presented in a similar manner. It is noted that the color values herein (e.g., a*, b*, L*) are calculated in accordance with the CIE LAB 1976 L*, a*, b* coordinate technique.
The IG units of Tables 1-2 (and thus Ser. No. 09/978,184) are not heat treated (HT). However, in commercial applications, at least some IG units often are required to be heat treated (e.g., tempered) for safety purposes. In office buildings for example, it is often desirable that some windows be heat treated while others need not be. Thus, a need for matchability (before heat treatment vs. after heat treatment) arises. In other words, it is desirable that window units which are heat treated (HT) substantially or approximately match their non-heat treated counterparts (e.g., with regard to color, visible transmission, reflectance, and/or the like), at least with respect to transmissive and glass side reflective optical characteristics, for architectural and/or aesthetic purposes.
Unfortunately, coatings of Ser. No. 09/978,184 cannot withstand HT without significant color and/or durability change. Thus, coatings of Ser. No. 09/978,184 cannot be HT and then used commercially to achieve matchability with their non-HT counterparts.
It will be apparent from the above that there exists a need in the art for coatings that, upon HT, approximately match non-HT coatings of Ser. No. 09/978,184 in the context of IG window units with regard to visible transmission, visible reflectance, transmissive color, and/or glass side reflective color.
While coatings having multiple infrared (IR) reflecting Ag layers are desirable in certain instances, they tend to have very low sheet resistance (Rs) values thereby making them difficult to easily HT (without resulting in damage or becoming prohibitively costly) using inexpensive HT processing/machinery. This is because the dual Ag layers tend to reflect much of the energy in the furnace intended for tempering the underlying glass substrate. Single silver coatings, with higher sheet resistances, are easier to HT in this regard. Thus, in certain example non-limiting instances it would be desirable for coatings herein to achieve the aforesaid matchability and/or be of the single Ag layer type (or have higher Rs) so that they can be more easily heat treated using conventional low-tech radiant tempering furnaces.
U.S. Pat. Nos. 5,514,476 and 5,800,933 discloses coated articles including: glass substrate/Si3N4/NiCr/Ag/NiCr/Si3N4. Unfortunately, upon HT and use in an IG unit, the resulting IG units do not approximately match the general aforesaid optical characteristics of IG units set forth in Table 2.
WO 02/04375 discloses a dual-silver low-E coating have good color characteristics after HT and lamination. Unfortunately, the coatings of WO 02/04375 require multiple silver (Ag) layers and have very low sheet resistance (Rs) (e.g., about 4-5 ohms/square) before HT. This makes the coatings of WO 02/04375 difficult to HT using conventional low-tech radiant tempering furnaces since the dual Ag layers reflect much of the energy intended for tempering the underlying glass substrate. It is noted that WO 02/04375 is a counterpart to U.S. Ser. No. 09/794,224, filed Feb. 28, 2001.
An object of certain example embodiments of this invention is to provide a coating that, upon HT and in the context of IG window units, approximately matches an IG unit including a non-HT coating of Ser. No. 09/978,184 (see general desired optical characteristics in Table 2 above) with respect to visible transmission (Tvis), visible glass side reflectance (RgY), transmissive color (a* and/or b*), and/or glass side reflective color (a* and/or b*).
Another object of certain example embodiments of this invention is to provide a single silver (Ag) coating (i.e., including only one Ag layer) that, upon HT and in the context of IG window units, approximately matches an IG unit including a non-HT coating of Ser. No. 09/978,184 with respect to visible transmission (Tvis), visible glass side reflectance (RgY), transmissive color (a* and/or b*), and/or glass side reflective color (a* and/or b*).
In certain example embodiments of this invention, it would be desirable for the coating, prior to HT, to have a sheet resistance (Rs) prior to HT of at least 8 ohms/square, more preferably of at least 10 ohms/square, and sometimes from about 11 to 20 ohms/square, so that the coating can be easily HT while on a supporting glass substrate in conventional low-tech radiant tempering furnaces. In certain example embodiments, the coating has only one Ag layer.
Another object of certain example embodiments of this invention is to provide a heat treatable coating that achieves certain desired color characteristics (whether corresponding to non-HT coatings of Ser. No. 09/978,184 or not) through the use of a layer comprising Si-rich (non-stoichiometric) silicon nitride.
Another object of certain example embodiments of this invention is to provide a heat treatable coating that includes a non-stoichiometric silicon nitride layer, wherein the amount of Si in the layer is adjusted (i.e., increased relative to stoichiometric Si3N4) so as to increase the layer""s index of refraction xe2x80x9cnxe2x80x9d and/or extinction coefficient xe2x80x9ckxe2x80x9d, in order to achieve desired optical characteristics.
Another object of this invention is to fulfill one or more of the above-listed objects and/or needs.
Certain example embodiments fulfill one or more of the above-listed objects and/or needs by providing an insulating glass (IG) window unit comprising first and second glass substrates spaced apart from one another so that a space is provided therebetween, at least the first glass substrate being thermally tempered and supporting a coating, wherein the coating comprises: a first dielectric layer comprising silicon nitride SixNy, a first contact layer, a layer comprising Ag, a second contact layer, wherein the layer comprising Ag is located between and directly contacts each of said first and second contact layers, and a second dielectric layer,
wherein the first dielectric layer comprising silicon nitride SixNy is Si-rich so that x/y is from 0.76 to 2.0, and so that after thermal tempering of the first substrate with the coating thereon the coating has a sheet resistance (Rs) of at least 7 ohms/square (7 or higher), and wherein the IG window unit has a visible transmission of at least 69%, transmissive a* color of from xe2x88x926.0 to 1.0, transmissive b* color of from xe2x88x921.0 to 4.0, glass side reflective a* color of from xe2x88x924.0 to 2.0, and glass side reflective b* color of from xe2x88x924.0 to 3.0.
Certain other example embodiments of this invention fulfill one or more of the above-listed objects and/or needs by providing an insulating glass (IG) window unit comprising: first and second glass substrates spaced apart from one another, the first glass substrate supporting a coating, wherein the coating comprises: a first dielectric layer comprising silicon nitride SixNy, only one layer comprising Ag, a second dielectric layer, and wherein the first dielectric layer comprising silicon nitride SixNy is characterized in that x/y is from about 0.76 to 2.0, and wherein the coating has a sheet resistance (Rs) of at least 6 ohms/square before and after heat treatment at temperature(s) of at least 500 degrees C.
Still further example embodiments of this invention fulfill one or more of the above-listed objects and/or needs by providing a method of making an IG window unit, the method comprising: forming a coating on a glass substrate so as to have a sheet resistance (Rs) of from 8 to 30 ohms/square before heat treatment, wherein the coating includes a layer comprising Ag and a dielectric layer comprising Si-rich silicon nitride having an index of refraction xe2x80x9cnxe2x80x9d of from 2.2 to 2.5 and an extinction coefficient xe2x80x9ckxe2x80x9d less than or equal to 0.06; thermally tempering the glass substrate having the coating thereon; and after the tempering, coupling the glass substrate with the coating thereon to another substrate to form an IG window unit having at least three of: (i) a visible transmission of at least 69%, (ii) transmissive a* color of from xe2x88x926.0 to 1.0, (iii) transmissive b* color of from xe2x88x921.0 to 4.0, (iv) glass side reflective a* color of from xe2x88x924.0 to 2.0, and (v) glass side reflective b* color of from xe2x88x924.0 to 3.0.
Yet other example embodiments of this invention fulfill one or more of the aforesaid objects and/or needs by providing a coated article comprising a glass substrate supporting a coating having a sheet resistance (Rs) of from 7 to 40 ohms/square before and/or after heat treatment, wherein the coating includes a layer comprising Ag and a dielectric layer comprising non-stoichiometric silicon nitride having an index of refraction xe2x80x9cnxe2x80x9d of from 2.2 to 2.5 and an extinction coefficient xe2x80x9ckxe2x80x9d less than or equal to 0.06.